A spokesman for Eastbourne District General Hospital told the BBC that 133 people had received treatment on Sunday.

Kyle Crickmore, who had been enjoying the Bank Holiday weekend sunshine at the beach at Birling Gap with his family, tweeted: "Some sort of chemical incident at Birling Gap, eyes are streaming and there's a strong smell of chlorine in the air".

He had finished swimming when his eyes started stinging. He looked around and saw everyone on the beach also rubbing their eyes and coughing in what he described as "all sorts of strange behaviour".

Sussex Police and East Sussex Fire Service are dealing with an incident in the Birling Gap area. (1/2)

He told BBC News: "Then looking out towards the water, there was just this crazy foggy haze rolling in off the sea out of nowhere. It was definitely out of the ordinary considering it was a nice clear sunny day 10 minutes beforehand.

"It was stupidly busy and it was a boiling hot day. It emptied in about 10 minutes which was quite staggering considering the amount of people who were there."

Members of the public alerted emergency services just before 5pm.

Members of the public are advised by Fire Service to stay indoors and shut windows if you are in the Eastbourne area. (2/2)

The RNLI said that "possibly some kind of gaseous fumes" had drifted over and a significant number of people on cliff tops had been struck down with symptoms including irritation, sore eyes and vomiting.

The RNLI launched all-weather lifeboats from Eastbourne and Newhaven to the Birling Gap area after fears from the coastguard that people could be trapped on the beach. There was a doctor on board the Eastbourne lifeboat.

UK Coastguard commander Steve Carson said: "This seems to have been caused by an unknown haze coming in from the sea, but the source has not yet been established. People living along the coast in the area have been advised by emergency services to keep doors and windows shut and to move away from the Birling Gap area in particular."

Eastbourne councillor Kathy Ballard described it as "a matter of definite concern," adding: "We need to find out the cause, where did this come from and to make sure that steps are taken so that it does not happen again. I have not heard of it happening before in this area."

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